This invention relates to an endoscope having a cassette removably incorporated in the forward section of an elongated sheath adapted to be inserted into the body cavity of a human being and having a film for photographing a desired portion of the body cavity of the human being.
A variety of endoscopes equipped with a cassette, a cartridge or a patrone (hereinafter referred to merely as a film cassette) are known in the art. Generally, the film cassette is incorporated in the forward section of a sheath of an endoscope by removing a metallic cap member threadably engaged with the front end portion of the sheath. With the cassette so incorporated an exposure window provided in a frame or housing of the cassette optically corresponds to a photographing window provided in the outer periphery of the forward section of the sheath. This type is called a side view type endoscope.
With the side view type endoscope equipped with a cassette, when the cassette is removed after film exposure from the forward section of the sheath, a cap member should be removed from the forward section of the sheath together with a cylindrical frame body having, for example, an observation window and illumination window which are optically coupled to an image guide fiber bundle and light guide fiber bundle in the longitudinal passage of the sheath. In the endoscope of this type parts of optical systems for photographing, observation and illumination and their supporting portions are exposed directly to an outer atmosphere, there being a fear that these parts or portions will be contaminated due to the deposition of dirt and dust etc. Since the frame body must be removed from the forward section of the sheath upon each removal of the cassette, the engaging portions of the parts are much worn, making it difficult to maintain liquidtightness and creating a clearance through which daylight is penetrated into a cassette receiving chanmber. As a result, there is a fear that a film will be unwarrantedly exposed by a daylight, that is, fogging will occur. Furthermore, a cumbersome operation is necessary in detachably incorporating the cassette into the forward section of the sheath.